(1) Field of the Invention
The present invention relates to tape transports and particularly to apparatus for causing movement of a magnetic recording tape relative to a recording and/or playback head. More specifically, this invention is directed to a hermetically sealed tape transport cartridge which minimizes the error rate of a magnetic tape system employed to store one or more programs, sets of instructions or other digital data.
(2) Description of the Prior Art
Tape transport mechanisms are, of course, well known in the art. Tape transports of the same general type as that to which the present invention is directed are exemplified by the apparatus disclosed in U.S. Pat. Nos. 3,620,473 and 3,974,982 which are assigned to the assignee of the present invention. A tape transport will typically include a tape handling mechanism, a magnetic tape on which a program may be stored, a read/write head and a drive motor. It is, of course, essential that the tape transport operate with very low error rate.
In the interest of minimizing error rate, the tape and transport parts must be maintained in a clean and dry state. Dirt will cause dropout errors on the tape. A high moisture content in the air, combined with a warm temperature, will cause deterioration of both the head and tape leading to rapid wear-out and an increasing error rate. If humid air is trapped within the unit, cooling can cause condensation of moisture on the tape and other parts, also leading to deterioration and continued cooling can cause freezing of the condensed moisture. Any ice which forms may cause the tape to separate from the head or may cause the mechanism to fail to drive. Thus, to permit use in a wide variety of environments, a tape transport should be suitable for hermetic sealing. Most prior tape transports have been belt or gear driven from a "remotely" located motor and thus hermetic sealing has been difficult.
Several mechanical and/or dynamic problems have also been encountered in some of the prior art. A typical arrangement may have a spring loaded idler to apply tension to a peripheral drive belt; and vibration forces may vary the load of the idler. Additionally, tape spillage resulting from unequal rates of acceleration and deceleration of the supply and take-up reels of a tape transport has been a prevalent prior art problem as has rotation of one reel with respect to the other, especially when power is suddenly removed from the drive motor.
Another deficiency of some prior art tape transports has resided in the fact that they have not provided for compensation for dimensional changes encountered when operating over a wide temperature range. Stability of operation over a wide temperature range is also essential to minimizing the error rate.
In high speed applications, the dangers of possible spillage or tape overstressing become acute. A particular and previously unsolved problem resides in the imbalance between the rotational kinetic energy of the supply and take-up reels. As a result of this imbalance, which varies as a function of the amount of tape on each reel at any instant, one reel of a tape transport will typically react faster or slower than the other thereby causing excess tension or slack. The tension stresses can, if sufficiently severe, cuase breaking of the tape; while slack may at the very least result in the movement of the tape away from the head thus causing an error.